Field of the Invention
The present invention relates to a technique to determine an amount of projection light in a measurement system.
Description of the Related Art
A technique for three-dimensional measurement of an object is known as an important technical element in the field of machine vision. One method of the three-dimensional measurement technique is an active method in which a distance is measured by projecting light onto a target object and measuring reflected light. As one example, there is a method of projecting two-dimensional pattern light onto a target object and capturing an image of corresponding reflected light (projection image) with a camera. In this method, the location of the projection image in the captured image is detected by referring to the characteristics of the two-dimensional pattern light. Then, with the use of the travelling direction of the pattern light and the direction of detection of the projection image, the distance is triangulated.
With the active method, higher contrast of the projection image in the captured image leads to more improvements in the location detection performance and realization of stable and high-accuracy distance measurement. It is thus desirable that the reflected light from the target object be within the dynamic range of a camera and be as intense as possible within this range.
Japanese Patent Laid-Open No. 2000-241131 describes obtainment of an average distance to a target object using a distance sensor and determination of the intensity of projection light based on the obtained distance. More specifically, according to the description of this document, the amount of projection light is increased if the distance from a projection apparatus to the target object is long, and decreased if the distance is short.